The present invention relates to a double-acting piston and more particularly to a measuring piston that is guided in a cylinder and arranged to be thrust upon on both sides thereof by a medium which pulsates at slight pressure differences, the average pressure of which is substantially the same, said piston having an elastic double lipped seal that includes mirror image sealing lips that extend toward one another. The oppositely extending sealing lips encompass an annular support member and thus form a piston that is attached to a piston rod, and together with the cylinder form an annular sealing chamber.
Pistons having double lipped seals constructed in this manner are usually availed of where very large pressure differences prevail on opposite sides of a piston and particularly where pressure chambers that are situated on the two sides of the piston are required to be most effectively sealed against leakage. The pressure built up with seals of this type in the annular sealing chamber formed by the mutually facing sealing lips presses the sealing lips against the cylinder wall and thereby form a good seal admittedly at a concurrently increased frictional resistance. Thus, in many cases, because the seal is so efficient it has been found that the sealing chamber pressure can lead to a jamming effect between the piston and the wall of the cylinder.
In measuring devices or other control devices in which small volume differences are to be detected at correspondingly small pressure differences, a double-acting piston can advantageously perform this function; however, the double-acting piston must work as leak-free as possible and with an exceedingly low frictional resistance so as not to falsify the measured results.
Measuring pistons which are fitted into a measuring cylinder with a clearance of a few thousandths of a millimeter and are set into motion by means of the fluid, without supplementary sealing means, and serve to indicate volume changes and pressure changes by means of optically measured changes in position, are well known. Such a measuring piston has the disadvantage of reacting very sensitively to dirt entrained in the measuring medium and a direct articulation of a non-contacting electrical excursion sensor as a consequence is not possible with such a structure.